The present invention relates to organic-inorganic composite particles, to a production process therefor and to liquid crystal displays which employ the organic-inorganic composite particles.
Liquid crystal displays (LCD) typically include two opposed electrode substrates, and spacers and a liquid crystal substance interposed between the aforementioned electrode substrates. The spacers are employed in order to maintain a liquid crystal layer uniform and constant in thickness.
High speed of response, high contrast, and a wide viewing angle, etc. are among display performance characteristics cited as required in practice in liquid crystal displays. For these performance characteristics to be manifested, the thickness of the liquid crystal layers, and in the final analysis the distance separating the two electrode substrates, must be maintained strictly constant.
Spacers for liquid crystal displays which meet such a need include silica particles made by the sol-gel method (Japanese Unexamined Patent Publication (Kokai) 62-269933), the calcined product of the aforementioned silica particles (Japanese Unexamined Patent Publication (Kokai) 1-234826), and styrene or divinylbenzene type polymer particles obtained by suspension polymerization of styrene monomers or divinylbenzene monomers, etc. (Japanese Unexamined Patent Publication (Kokai) 61-95016), etc. These are all spherical particles with a narrow particle diameter distribution and a well ordered particle diameter.
However, the above prior art has the following problems.
(A) Calcined products of silica particles made by the sol-gel method are not readily deformable and are very hard, and consequently when they are pressed in constructing liquid crystal displays they may cause physical damage to coating layers on the substrates such as vapor deposited electrodes, etc., orientating layers and color filters, etc., and cause faults in the display due to image unevenness or breakages of TFT array. There is also a large difference between the thermal expansion coefficient of these calcined silica particles and that of liquid crystals, and consequently in liquid crystal displays using such calcined silica particles the problem of so-called low-temperature bubbling is produced, so that when cooled in a low temperature environment, of -40.degree. C. for example, the particles do not shrink to the same extent as the liquid crystals; voids are produced between the liquid crystals and the electrode substrates, and the display function becomes completely inoperative.
(B) Silica particles made by the sol-gel method are more pliant than calcined silica particles. However, because these uncalcined silica particles are weak in mechanical resilience the gap distance is prone to become uneven, producing image unevenness. Moreover, uncalcined silica particles give rise to the low-temperature bubbling problem as well as the calcined silica particles do.
(C) Since styrene or divinylbenzene type polymer particles are organic particles and are very pliant, they must be dispersed in large numbers onto an electrode substrate. This not only tends to raise manufacturing costs, but results in an increase in the area of the portion of the display screen where no image is formed. Moreover, the quality of the display is lowered due to lowering contrast and increasing image roughness, etc. due to the fact that the quantity of ionic and molecular impurities eluting from the spacers into the liquid crystal layer increases.
Accordingly, polymer particles have been proposed which are not easily deformed, formed by suspension polymerization using crosslinkable monomers such as divinylbenzene, etc., and using a large quantity of polymerization initiator (Japanese Unexamined Patent Publication (Kokai) 4-313727).
Polymer particles made by suspension polymerization of tetramethylolmethane tetraacrylate or tetramethylolmethane tetraacrylate and divinylbenzene, and then classified to regulate mean particle diameter and standard deviation of particle diameter have also been proposed (Japanese Patent Publication (Kohyo) 6-503180).
These polymer particles have the problem that they are prone to produce abnormal orientation in the liquid crystals on the surfaces of these particles. In liquid crystal displays no display is possible in spots in which the liquid crystals are abnormally orientated.
The present inventors have proposed spacers for liquid crystal displays which have a residual displacement after 10% deformation and an elastic modulus in compression at the 10% displacement of the particle diameter (an elastic modulus in 10% compression) within specified ranges, and which includes specific organic-inorganic composite particles (Japanese Patent Application 5-288536). The fact that these spacers for liquid crystal displays are harder than prior polymer particles means that the number of the particles dispersed on the electrode substrate can be decreased. However, the decrease in numbers means that the load per particle is increased, and the fracture strength is inadequate.
Prior electrically conductive particles are inorganic particles such as silica particles, etc., or polymer particles provided with a conductive layer formed on the surface of the particles. Commonly, conductive particles are employed in the electronics field for connecting between pairs of electrodes. Thus, by pressing a pair of electrodes with conducting particles interposed between them, an electrical connection is established between the two electrodes via the conductive particles.
Conductive particles including a polymer are too pliant, consequently when pressed the conductive layer cannot accompany the deformation of the particles, and the conductive layer may detach and fall from the particle surface, the electrodes may become too close and short. On the other hand, conductive particles including inorganic particles are too hard, and consequently it is impossible to broaden the area of contact with the electrodes to lower contact resistance, and if unreasonable pressure is applied when deforming so as to get large contact area, the conductive layer may detach and fall away. There are also problems the poor mechanical resilience of the conductive particles, and it becomes difficult to maintain a constant gap distance, causing poor contact.